U.S. patent number 4,274,908 [Application Number 06/150,276] was granted by the patent office on 1981-06-23 for cyanide free solution and process for removing gold-nickel braze.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to Robert E. Fishter, Brian A. Manty.
United States Patent |
4,274,908 |
Fishter , et al. |
June 23, 1981 |
Cyanide free solution and process for removing gold-nickel
braze
Abstract
An effective cyanide free solution and process for removing
gold-nickel braze alloys from superalloy parts are described. The
solution contains about 50% nitric acid with intentional additions
of materials which ionize to provide chloride ions, sulfate ions,
and metal ions in specific concentrations.
Inventors: |
Fishter; Robert E. (Boca Raton,
FL), Manty; Brian A. (Lake Park, FL) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
26847502 |
Appl.
No.: |
06/150,276 |
Filed: |
May 15, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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933944 |
Aug 15, 1978 |
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Current U.S.
Class: |
216/90; 216/108;
252/79.2; 75/715 |
Current CPC
Class: |
C23F
1/44 (20130101) |
Current International
Class: |
C23F
1/44 (20060101); C09K 013/04 (); C23F 001/00 () |
Field of
Search: |
;156/637,638,664
;252/79.2 ;75/97A,11R,104,118R,118P,119 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Flitsch, "Etch for Removing Gold" IBM Technical Disclosure Bulletin
vol. 10, No. 4, (9/67) p. 355..
|
Primary Examiner: Massie; Jerome W.
Attorney, Agent or Firm: Sohl; Charles E.
Government Interests
The invention herein described was made in the course of or under a
contract or subcontract with the Department of the Air Force.
Parent Case Text
This is a continuation of application Ser. No. 933,944 filed on
Aug. 15, 1978, now abandoned.
Claims
Having thus described a typical embodiment of our invention, that
which we claim as new and desire to secure by Letters Patent of the
United States is:
1. A method for removing gold-nickel type braze material from
brazed metallic articles selected from the group consisting of
stainless steels, cobalt superalloys and nickel superalloys,
without significant base metal attack consisting of:
immersing the brazed articles in a heated aqueous solution which
contains from about 40 to about 50% concentrated nitric acid, about
0.01 to about 0.1 mole/l sulfate ions, from about 0.005 to about
0.2 mole/l chloride ions, and at least about 0.001 mole/l metal
ions, said solution being held at a temperature between about
75.degree. and 150.degree. F., for a period of time sufficient to
remove the braze without adversely affecting the metallic
article.
2. A process as in claim 1 wherein the solution is ultrasonically
agitated to increase the rate of braze material removal.
3. A method as in claim 1 wherein the metal ions are selected from
the group consisting of copper, iron, nickel, chrome, cobalt,
cerium and sodium and mixtures thereof.
4. A method as in claim 1 wherein the sulfate ion concentration is
derived from sulfuric acid and the chloride ion concentration is
derived from a metal chloride.
5. A method as in claim 1 wherein the sulfate ion concentration is
derived from a metal sulfate and the chloride ion concentration is
derived from HCl.
6. A method as in claim 1 wherein the solution contains nitric
acid, copper sulfate and ferric chloride.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to solutions and processes for chemically
removing braze alloys from superalloy parts.
2. Description of the Prior Art
It is known in the art to remove various braze alloys including
gold-nickel braze alloys from various substrate alloys using
cyanide containing alkaline solutions. At least one patent, U.S.
Pat. No. 3,958,984, teaches the use of a cyanide containing
alkaline solution in combination with a second acid solution.
In a somewhat different art area, U.S. Pat. Nos. 3,399,143 and
3,367,874 relate to the removal of nickel plate from articles such
as plating racks. U.S. Pat. No. 3,856,694 teaches the use of a
nitric acid solution containing chloride, copper and tellurium or
selenium ions to remove nickel plate from plating apparatus.
SUMMARY OF THE INVENTION
A method is described for removing a gold-nickel braze alloy from
superalloy parts. The method employs a solution which contain from
about 30 to about 60% nitric acid, 0.005 to 0.15 moles per liter
sulfate ions, and from 0.001 to 0.4 moles per liter chloride ions.
The chloride and sulfate ions are preferably derived from metal
salts. Metal ions are preferably present in the solution in
concentrations of at least about 0.001 moles/liter. This solution
is used at a temperature of about 120.degree.-150.degree. F. and
the part from which the braze is to be removed is immersed in the
solution for a period of several hours. Ultrasonic agitation may be
used to accelerate the process. The process has been found to be
effective in removing gold-nickel braze alloys from a variety of
nickel and cobalt superalloy and stainless steel substrates without
any measurable substrate attack.
The foregoing and other objects, features and advantages of the
present invention will become more apparent in the light of the
following detailed description of preferred embodiments
thereof.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention relates to a process and solution for
removing certain braze alloys from superalloys and stainless steel
parts. The process is cyanide free and thus is desirable from
environmental and employee safety points of view. The solution is
also quite specific to the gold-nickel braze alloys and produces no
measurable attack of the parts from which the braze material is
being removed. Specific braze alloys which have been successfully
removed by the present invention are those based on gold which
contain from about 10 to about 30% nickel. Specific braze alloys
are listed in Table I. Braze alloys of these compositions have
successfully been removed from a variety of nickel base superalloys
including those whose compositions are listed in Table II.
Gold-nickel braze has also been removed from cobalt base alloys
whose compositions are listed in Table II. Finally, a successful
removal of gold-nickel braze material from stainless steels of the
410 and 347 types has been achieved.
The essential ingredients of the solution include from 30 to 60%
nitric acid by weight, from 0.005 to 0.15 moles per liter of
sulfate ions and from 0.001 to 0.4 moles per liter of chloride
ions, balance water. The preferred ranges are 40 to 50% nitric
acid, 0.01 to 0.1 moles per liter sulfate and 0.005 to 0.2 moles
per liter chloride ions. These ions are preferably obtained from
ionizable metal containing compounds and preferably metal ions are
present in the solution in concentrations of at least 0.001 moles
per liter and preferably 0.05 moles per liter. Solutions in which
the chloride and sulfate ions are derived from acids such as
hydrochloric and sulfuric have been evaluated. Such solutions must
be rather dilute if base metal attack is to be avoided and,
therefore, these solutions are slow acting. Solutions which contain
metal ions can be more concentrated without causing base metal
attack. Consequently, these solutions remove braze metal more
rapidly and thus are preferred.
It is believed that the nitric acid and chloride ions dissolve the
gold constituent of the braze material in a fashion similar to the
way in which aqua regia dissolves gold. The nitric acid dissolves
the nickel component of the braze material. It is believed that the
sulfate ion may form a complex with the gold thereby speeding the
rate of dissolution.
TABLE I ______________________________________ AMS No. Au Pd Ni
______________________________________ 4784 50 25 25 4785 30 34 36
4786 70 8 22 4787 82 -- 18
______________________________________
TABLE II
1. Waspalloy: 0.07 C, 19.5 Cr, 13.5 Co, 4.3 Mo, 3 Ti, 1.4 Al, 0.006
B, 0.09 Zr, Bal Ni.
2. Hastelloy X: 0.1 C, 0.5 Mn, 0.5 Si, 22 Cr, 1.5 Co, 9 Mo, 0.6 W,
18.5 Fe, Bal Ni.
3. IN 100: 0.18 C, 10 Cr, 15 Co, 3 Mo, 4.7 Ti, 5.5 Al, 0.014 B,
0.06 Zr, 1 V, Bal Ni.
4. MAR-M-200: 0.15 C, 9 Cr, 10 Co, 12.5 W, 1 Cb, 2 Ti, 5 Al, 0.015
B, 0.05 Zr, Bal Ni.
5. Astrolloy: 0.06 C, 15 Cr, 15 Co, 5.25 Mo, 3.5 Ti, 4.4 Al, 0.03
B, Bal Ni.
6. Inconel 625: 0.05 C, 22 Cr, 9 Mo, 4 Cb, 0.2 Ti, 0.2 Al, 3 Fe,
Bal Ni.
7. Inconel 718: 0.04 C, 18.6 Cr, 3.1 W, 5 Cb, 0.9 Ti, 0.4 Al, 18.5
Fe, Bal Ni.
8. Inconel X750: 0.04 C, 15 Cr, 0.9 Cb, 2.5 Ti, 0.8 Al, 6.8 Fe, Bal
Ni.
9. L 605: 0.1 C, 20 Cr, 10 Ni, 15 W, Bal Co.
10. Haynes 188: 0.1 C, 22 Ni, 22 Cr, 14.5 W, 0.075 La, Bal Co.
11. 347 SS: 0.05 C, 18 Cr, 11 Ni, 0.5 Cb+Ta, Bal Fe.
12. 410 SS: 0.1 C, 12.5 Cr, Bal Fe.
13. Greek Ascoloy: 0.17 C, 13 Cr, 2 Ni, 3 W, Bal Fe.
The braze removal process uses the previously described solution at
a temperature of about 75.degree.-150.degree. F. and preferably at
a temperature of about 140.degree. F. Lower temperatures reduce the
reaction rate considerably while at higher temperatures the
solution becomes depleted in nitric acid by reason of
evaporation.
This braze removal process is particularly useful in the
refurbishment of gas turbine engine parts. Certain engine parts are
fabricated and assembled by brazing and some such brazed parts may
become worn or damaged in service.
Ultrasonic agitation of the solution has been found to accelerate
the braze removal process and hence ultrasonic agitation is
preferred for reasons of economy. The present invention may be
better understood by reference to the following examples which are
meant to be illustrative rather than limiting.
The following examples show the effectiveness of various solution
compositions within the scope of the present invention. The
examples deal with tests performed on sections of a turbine stator
fabricated from Inconel 718 brazed together with a braze compound
of 82% gold and 18% nickel. The examples were performed in
solutions held at a temperature of 140.degree. F. and the solutions
were ultrasonically agitated at a frequency of 18.5 Khz and a power
density of about 1 watt/cm.sup.2 into a 1 liter container of the
solution. All of the solutions contained 500 ml/l of concentrated
nitric acid, approximately an 8 molar concentration.
EXAMPLE I
A solution was made up containing 2.5 g/l of copper sulfate and 1.3
g/l ferric chloride in the 8 molar nitric acid base. This solution
produced an SO.sub.4 concentration of 0.01 mole/l, a Cl
concentration of 0.005 mole/l, a Cu concentration of 0.01 mole/l,
and an Fe concentration of 0.005 mole/l. This solution completely
removed the braze material without attacking the base material in 6
hours. The base material was left in the solution for an additional
24 hours and microscopic examination did not reveal any evidence of
base metal attack.
EXAMPLE II
A solution was made up containing 5.0 g/l nickel sulfate and 0.3
g/l ferric chloride in the 8 molar nitric acid base. This solution
produced an SO.sub.4 concentration of 0.02 mole/l, a Cl
concentration of 0.001 mole/l, a Ni concentration of 0.02 mole/l,
and an Fe concentration of 0.001 mole/l. This solution completely
removed the braze material without attacking the base material in 6
hours. The base material was left in the solution for an additional
24 hours and microscopic examination did not reveal any evidence of
base metal attack.
EXAMPLE III
A solution was made up containing 2.1 g/l H.sub.4
Ce(SO.sub.4).sub.4 and 2.1 g/l CrCl.sub.3 in the 8 molar nitric
acid base. This solution produced a SO.sub.4 concentration of 0.015
mole/l, a Cl concentration of 0.008 mole/l, a Ce concentration of
0.006 mole/l and a Cr concentration of 0.004 mole/l. This solution
completely removed the braze material within 20 hours with
negligible base material attack.
EXAMPLE IV
A solution was made up containing 4.45 g/l CoSO.sub.4 and 2.1 g/l
CoCl.sub.2 in the 8 molar nitric acid base. This solution produced
a SO.sub.4 concentration of 0.010 mole/l, a Cl concentration of
0.008 mole/l, and a Co concentration of 0.016 mole/l. This solution
completely removed the braze material within 20 hours with
negligible base material attack.
EXAMPLE V
A solution was made up containing 5.1 g/l NaSO.sub.4 and 1.4 g/l
NaCl in the 8 molar nitric acid base. The solution produced a
SO.sub.4 concentration of 0.004 mole/l, a Cl concentration of 0.008
mole/l, and a Na concentration of 0.01 mole/l. This solution
completely removed the braze material within 20 hours with
negligible base material attack.
EXAMPLE VI
A solution was made up containing 2.7 g/l CuSO.sub.4 and 0.8 g/l
FeCl.sub.3 in the 8 molar nitric acid base. This solution produced
a SO.sub.4 concentration of 0.016 mole/l, a Cl concentration of
0.005 mole/l, a Cu concentration of 0.010 mole/l and a Fe
concentration of 0.003 mole/l. This solution completely removed the
braze material within 20 hours with negligible base material
attack.
EXAMPLE VII
A solution was made up containing 5 g/l CuSO.sub.4 and 10 ml/l HCl
in the 8 molar nitric acid base. This solution produced a SO.sub.4
concentration of 0.030 mole/l, a Cl concentration of 0.12 mole/l,
and a Cu concentration of 0.020 mole/l. This solution completely
removed the braze material within 20 hours with minimal attack on
the base material. This example illustrates that HCl may be used as
a source of Cl ions.
EXAMPLE VIII
A solution was made up containing 2.5 ml/l H.sub.2 SO.sub.4 and 3.0
g/l FeCl.sub.3 in the 8 molar nitric acid base. This solution
produced a SO.sub.4 concentration of 0.045 mole/l, a Cl
concentration of 0.020 mole/l, and an Fe concentration of 0.010
mole/l. This solution completely removed the braze material within
20 hours with negligible attack on the base material. This example
illustrates that the SO.sub.4 ion may be derived from H.sub.2
SO.sub.4.
EXAMPLE IX
A solution was made up containing 1 ml/l H.sub.2 SO.sub.4 and 1
ml/l HCl in the 8 molar nitric acid base. This solution produced a
SO.sub.4 concentration of 0.018 mole/l, a Cl concentration of 0.012
mole/l, with no metal ions present. This solution partly removed
the braze material within 20 hours with negligible base metal
attack. This example, in conjunction with Examples VII and VIII
illustrates the benefits resulting from the inclusion of metal ions
in the solution.
EXAMPLE X
A solution was made up containing 5 g/l Fe.sub.2 (SO.sub.4).sub.3
and 3.0 g/l CrCl.sub.3 in the 8 molar nitric acid base. This
solution produced a SO.sub.4 concentration of 0.023 mole/l, a Cl
concentration of 0.020 mole/l, a Fe concentration of 0.027 mole/l
and a Cr concentration of 0.010 mole/l. This solution completely
removed the braze material within 12 hours with negligible base
metal attack.
The preceding examples have shown that the solutions of the
invention can be effective when made up from a wide variety of
metal salts. Examples have further shown that an acid may be
substituted for one of the salts without adversely affecting the
effectiveness of the solution. For commercial reasons and because
of its ready availability, solutions based on ferric chloride and
copper sulfate are preferred. These solutions have previously been
described in Examples I and VI. Solutions based on ferric chloride
and copper sulfate with nitric acid have been used to remove
gold-nickel braze from Waspalloy, Greek Ascoloy, Type 347 Stainless
Steel and Haynes 188. Based on past experiences, it is anticipated
that these solutions would be equally successful in removing
gold-nickel braze material from Type 410 Stainless Steel, Hastelloy
X, Inconel 625, Inconel X750, Astrolloy, IN 100, MAR-M-200 and
other similar alloys.
Although this invention has been shown and described with respect
to a preferred embodiment thereof, it should be understood by those
skilled in the art that various changes and omissions in the form
and detail thereof may be made therein without departing from the
spirit and scope of the invention.
* * * * *